In the manufacture of photographic dispersions, photographically useful compounds are dispersed in an aqueous medium containing a hydrophilic colloid, such as gelatin. The photographically useful compound may be a liquid which may be dispersed directly into the aqueous medium or it may be a solid or liquid predissolved in an organic solvent. Typically, the photographically useful compound is dissolved in a permanent organic solvent, optionally with the use of an auxiliary solvent which assists dissolution of the photographically useful compound in the permanent solvent. The photographically useful compound or solution thereof is mixed under high shear or turbulence together with the aqueous medium, which may also contain a surfactant, in order to break the organic phase into submicron particles dispersed in a continuous aqueous phase. The auxiliary solvent, if present, is then removed by evaporation, washing or dialysis. The resulting dispersion comprises an aqueous medium containing a dispersed liquid organic phase comprising particles containing the photographically useful compound.
The resulting dispersion can be coated onto a support or incorporated into a silver halide emulsion or other photographic composition which is then coated onto a support. Generally a photographic element comprises a plurality of layers, at least one of which comprises a silver halide emulsion, coated onto a support. During, or just prior to, the coating step the dispersion may be heated to about 45.degree. C. and maintained at that temperature for up to 24 hours. It has been noted that in certain instances the dispersed particles containing the photographically useful compound can undesirably grow in the dispersion. This particle growth can cause the photographically useful material to become less effective for its intended purpose. For example, a dispersion containing relatively large particles of an ultra violet (UV) absorber may absorb less UV radiation (i.e., have a lower covering power) than a comparable smaller particle UV absorber dispersion. Similarly, dispersions containing an oxidized developer scavenger of undesirable large particle size may result in the dispersion scattering more light which may lead to granularity increases, sharpness losses, and/or density losses in the coated photographic element. In addition, if the particle growth is severe enough for extremely large particles (greater than 5 .mu.m in diameter) to be formed, the particles themselves may be visible in magnified prints or projections representing a physical defect in the coated photographic product.
Other photographically useful compounds which may exhibit undesirable particle growth include, for example, organic liquids which improve the scratch-resistance or pressure sensitivity of photographic materials during handling and mechanical transfer operations, or modify the reactivity of compounds of the layers, etc; optical brighteners; incorporated developers; anti-fogging agents; and the like.
An attempt to slow the particle growth in photographic dispersions is disclosed in U.S. Pat. No. 4,181,527 to Toda et al. Toda et al disclose that incorporation of organic solvent gelling agents, such as N-acylamino acid amides, N-acylamino acid amine salts, and dehydrated condensates of benzaldehydes and sorbitol or xylitol, into a photographic dispersion solidifies or "gels" the oil phase of the dispersion, thereby inhibiting particle growth. While this method does slow particle growth, the resulting viscosity increase of the dispersed phase containing the photographically useful compound can result in undesired decreases in performance such as reactivity or lubricity.